Re: RM and abstract syntax trees

On Nov 1, 1:31 pm, Jonathan Leffler <jleff..._at_earthlink.net> wrote:
> Marshall wrote:
> > On Oct 31, 7:50 pm, David BL <davi..._at_iinet.net.au> wrote:
> >> Isn't it helpful to see the analogy with a pointer dereference?
>
> >> I'll leave it up to you as to whether you dislike the analogy between
> >> node identifiers and pointer values, and the idea that a join can be
> >> compared to a pointer dereference. Perhaps you are right and the
> >> analogy creates confusion.
>
> > I think if we are clear about it being an analogy we are on solid
> > ground. But as soon as we start thinking pointers and references
> > are the *same* thing we are in trouble, because now we can't
> > see the differences anymore.
>
> > I think Date actually nails this issue. He says (roughly) that
> > pointers add complexity but don't add any expressive power.
>
> Isn't the other 'point' that 'pointers point somewhere' but values
> stored in a relation don't - that relational database bases work on
> associative addressing. In particular, even in a foreign key, the value
> doesn't point to the referenced primary key; it merely contains the same
> value as some entry in the referenced table. It may also contain the
> same value as a large number of other places in the database.

That's quite right, but note in the special case of using RM to represent an AST, a foreign key node identifier ends up uniquely referencing precisely one tuple in one relation elsewhere in the DB. Received on Thu Nov 01 2007 - 11:19:54 CET